1. Field of Invention
The present invention relates to an impedance matching method of a signal transmission path in a circuit board, and more particularly, to a calibration method of insulating washer in a circuit board.
2. Related Art
In the current design of a high-speed signal circuit board, electric signals in different signal layers are connected through a metal via, and the impedance characteristic achieved by a geometric structure of the circuit board usually does not match with the impedance characteristic of the signal lines for the signal layer. As a result, the signal reflection phenomenon easily occurs when a signal passes through the metal via, thereby degrading the signal transmission quality.
With reference to Taiwan Patent Publication No. 200612803, it discloses a double-layer printed circuit board (PCB) capable of controlling impedance and a method thereof. The double-layer PCB includes a dielectric layer and a plurality of high-speed signal transmission lines disposed on the dielectric layer, wherein ground layers are further disposed on the dielectric layer adjacent to each of the high-speed signal transmission lines. When the double-layer PCB is employed, a two-dimensional sectional view of the double-layer PCB is inputted into simulation software that calculates the characteristic impedance value of the high speed signal transmission lines and then compares it with a standard impedance value. Then, after the parameter values of the high-speed signal transmission lines and the relative position of the high-speed signal transmission lines and the ground layer have been adjusted for many times, the two-dimensional graph has been inputted for many times, and the simulation software has performed the calculation for many times, an ideal characteristic impedance value is obtained.
Although the above patent application has disclosed a method for controlling the impedance of a double-layer PCB, but through the method, the impedance of the multi-layer PCB with the metal via cannot be controlled. Therefore, the application of the aforementioned method is limited.
Therefore, how to provide a calibration method of insulating washer in a circuit board has become an urgent issue for being solved by researchers, so as to match with the impedance of the signal transmission lines in a multi-layer PCB.